The present invention relates to a piezo-oscillator, and more particularly, to a small piezo-oscillator having excellent aging characteristics.
In recent years, as communications equipment is reduced in size, a reference signal source used for the equipment is required to be small in size, and a quartz oscillator shown in FIG. 5 for example has been proposed.
FIG. 5(a) is a sectional view of a structure of a conventional quartz oscillator, and FIG. 5(b) is a circuit diagram of the conventional quartz oscillator.
As shown in FIG. 5(a), the quartz oscillator 100 includes an integrated amplifier circuit 101, a quartz vibrator 102, a ceramic container 103 having a recess for accommodating the amplifier circuit 101 and the quartz vibrator 102 therein, and a metal lid 104. After the amplifier circuit 101 is mounted in on a bottom surface of the recess of the ceramic container 103, the quartz vibrator 102 is mounted such as to cover an upper surface of the amplifier circuit 101, and the ceramic container 103 is sealed by the lid 104 such as to cover these members.
The quartz vibrator 102 and other electron parts are mounted in the common accommodation container in this manner, thereby realizing a compact quartz oscillator 100.
However, with the above structure, it is impossible to check a drive level dependence characteristics (DLD characteristics, hereinafter) such as variation in oscillation frequency with respect to drive level variation of the quartz vibrator 102.
That is, the DLD characteristics may be varied due to variation in producing procedure and producing conditions or the like.
Since the DLD characteristics affects the stability of frequency and characteristics and reproducibility of the quartz vibrator 102, it is indispensable to check the vibrator after it was completed.
A common method for checking the DLD characteristics of the quartz vibrator 102 is to change the drive level of the quartz vibrator 102 incorporated in the oscillator, and to check deviation of oscillation frequency with respect to variation of the drive level.
In the case of the quartz oscillator 100, since the quartz vibrator 102 and the amplifier circuit 101 are accommodated in the same container, the quartz vibrator 102 alone can not be checked. It seems possible to control a voltage value of a power source Vcc to be supplied to the oscillator circuit of the quartz oscillator 100, thereby adjusting the amplification action of the amplifier circuit 101 to control the drive level of the quartz vibrator 102.
However, since the quartz oscillator 100 output stable frequency signal even if the supplied power source voltage is varied, at least one of a constant-voltage circuit 105 and a constant-current circuit 106 is provided in the oscillator circuit as shown in FIG. 5(b) in many cases.
Therefore, in the case of the quartz oscillator 100 having such a structure, even if the power source voltage value is controlled, since the drive level of the quartz vibrator 102 is not varied, there is a problem that DLD characteristics can not be checked.
The present invention has been accomplished to solve the above problems of the conventional constant-voltage oscillator, and it is an object of the invention to provided a small quartz oscillator in which the DLD characteristics can be measured after it is packaged even if a constant-voltage circuit or constant-current circuit is included in the circuit.
To achieve the above object, according to the invention described in a first aspect, there is provided a piezo-oscillator comprising an oscillator circuit including a piezo-vibrator and an amplifier circuit, and a constant-voltage circuit, in which a power source and the oscillator circuit are connected through the constant-voltage circuit to supply a constant voltage to the oscillator circuit, wherein when a voltage of the power source is equal to or higher than a predetermined value, a function of the constant-voltage circuit is invalidated.
According to a second aspect, there is provided a piezo-oscillator comprising a piezo-oscillator including a piezo-vibrator, an amplifier circuit and a constant-current circuit, wherein when a voltage of the power source is equal to or higher than a predetermined value, a function of the constant-current circuit is invalidated.
According to a third aspect, there is provided a piezo-oscillator comprising an oscillator circuit including a piezo-vibrator and an amplifier circuit, a constant-voltage circuit and frequency control voltage section, in which a power source and the oscillator circuit are connected through the constant-voltage circuit to supply a constant voltage to the oscillator circuit, wherein when a voltage to be supplied to the frequency control voltage section is equal to or higher than a predetermined value, a function of the constant-voltage circuit is invalidated.
According to a fourth aspect, there is provided a piezo-oscillator comprising a piezo-oscillator including a piezo-vibrator, an amplifier circuit, a constant-current circuit and a frequency control voltage section, wherein when a voltage to be supplied to the frequency control voltage section is equal to or higher than a predetermined value, a function of the constant-current circuit is invalidated.
According to a fifth aspect, in addition to the first or the third aspect, within in a voltage range in which the function of the constant-voltage circuit is invalidated, the power source voltage is controlled, and a drive level of the piezo-vibrator is controlled by changing a voltage to be supplied to the amplifier circuit.
According to a sixth aspect, in addition to the second or the fourth aspect, within in a voltage range in which the function of the constant-voltage circuit is invalidated, the power source voltage is controlled, and a drive level of the piezo-vibrator is controlled by changing a voltage to be supplied to the amplifier circuit.
According to a seventh aspect, in addition to the fifth or the sixth aspect, it is possible to confirm drive level dependency characteristics of the piezo-vibrator by controlling a drive level of the piezo-vibrator.
According to an eighth aspect, there is provided a piezo-oscillator comprising an oscillator circuit including a piezo-vibrator and an amplifier circuit for supplying electric power to the oscillator circuit through a constant-voltage circuit or a constant-current circuit, wherein the constant-voltage circuit or the constant-current circuit is provided with a current bypass switch, a function of the constant-voltage circuit or the constant-current circuit is invalidated by controlling the switch from outside.